This invention relates to a compound semiconductor single crystal and a fabrication process for a compound semiconductor device and particularly, to a fabrication process for a compound semiconductor device in which a pattern is efficiently formed on a surface of a compound semiconductor single crystal with no resist coating.
Many devices such as a photodetector, a light emitting device, a high frequency device and a power device have recently been researched and developed, exploiting various characteristics of compound semiconductors. In fabrication of such compound semiconductor devices, for example, for such as electrode formation and integrated circuit formation, there has generally been adopted a process in which a prescribed pattern is formed on a surface of a compound semiconductor single crystal by a lithographic method to repeat resist coating and exposure.
In this process, however, as shown in conventional steps of FIG. 6, the following steps have been required: resist coating wherein a resist 2 is coated on a surface of a compound semiconductor single crystal 4 on which a silicon oxide film (SiO2) or a silicon nitride film (SiNx) has been deposited, while rotating the single crystal 4 at a high speed (STEP 1, FIG. 6(A)); then pre-bake wherein solvent and water are got out of the resist film 2 (STEP 2); exposure wherein a pattern 6 is printed on the resist film 2 under an ultraviolet light (STEP 3, FIG. 6(B)); development and rinsing wherein the pattern 6 is formed in the resist film 2 (STEP 4, FIG. 6(C)); post-bake wherein a developer and a rinsing liquid is removed from the resist film 2 (STEP 5); and thereafter, etching wherein the oxide film or the nitride film corresponding to the opening pattern 6 is removed by etching (STEP 6).
Thus, since many steps are required for forming a pattern 6 using the lithographic method in which resist coating and light exposure are repeated and a considerable cost is imposed on each step, there is a limitation on cost down as far as this method is employed.
Further, an influence cannot be neglected on damage of the crystal due to the deposition of the oxide film or the nitride film on the crystal surface and thereby the devices may be affected adversely in terms of their operation. In order to solve a problem of the damage, there has been recently proposed and practiced a method to use as a mask material a natural oxide film on a compound semiconductor readily oxidizable, such as AlGaAs. In this method, however, since such a lithographic method as above described is still adopted, a lot of steps are also required and it is difficult to reduce the number of the steps any more.
The present invention has been made in view of the above problems, and therefore an object of this invention is to provide a compound semiconductor single crystal and a fabrication process for a compound semiconductor device capable of forming a prescribed pattern without requirement of resist coating.
In order to solve the above problems, according to the present invention, there is provided a compound semiconductor single crystal, wherein a III-V compound semiconductor single crystal or a II-VI compound semiconductor single crystal includes a region in which a group V element component or a group VI element component is less than a composition ratio expressed by a chemical formula of a corresponding compound semiconductor single crystal.
Further, a fabrication process for a compound semiconductor device of the present invention comprises: a transmuting step of transmuting part of a surface of a III-V compound semiconductor single crystal or a II-VI compound semiconductor single crystal into a pattern-shaped portion by reducing a group V element component in the III-V compound semiconductor single crystal, or a group VI element component in the II-VI compound semiconductor single crystal less than a composition ratio expressed by a chemical formula of a corresponding compound semiconductor single crystal; and an etching step of effecting selective etching on the corresponding compound semiconductor single crystal.
The transmuting step is accomplished by imparting energy on the surface of the compound semiconductor single crystal to heat it. Further, the transmuting step may be accomplished by irradiating a laser beam or an electron beam on the surface of the compound semiconductor single crystal. Still further, in the etching step, the surface of the compound semiconductor single crystal transmuted in the transmuting step is preferably used as a protective film.
Also, a fabrication process for a compound semiconductor device of the present invention comprises: a growth step of forming a III-V compound semiconductor single crystal layer or a II-VI compound semiconductor single crystal layer on a semiconductor single crystal substrate; a transmuting step of irradiating a laser beam on a surface of the compound semiconductor single crystal layer to transmute the surface; and an etching step of effecting selective etching on the compound semiconductor single crystal layer having a region transmuted in the transmuting step to form a protective film.
The laser beam preferably has energy larger than a bandgap of the compound semiconductor single crystal layer to be irradiated with the laser beam. Further, irradiation power of the laser beam is preferably in the range of from 1 kW/cm2 to 5 kW/cm2.